Maybe it could work like this:
In every bank, there is another person, in bankers uniform, but he isnt behind the counter. For now, call him bob.
Bob is a sales executive person. You can give him items and set a price you want for them, and then other players can come along and see all the items up for sale and their prices, and they can then buy them. When you go back to him, if your items havent sold, you can get the back, and if they have, you can get the money for them.
If another player talks to bob, they can view all the items up for sale from everyone in every world. Because of the obvious extreme numbers of items there would be, there would probably be a search function. For example, if you searched for "death runes" you would get all the death runes anyone was offering for sale, and all the different prices for them, and players could choose which ones to buy for the cheapest price.
When buying something, it would also say the player's name, but they could choose to stay anonymous if they so wished.
I made some fakes to illustrate my idea:
I personally think this would be good, as it would allow players to keep playing, and not have to clog up world 1 selling stuff. It may also help to stabilise the economy, but then again, i spose its possible it could crash it.